Conventional planar light sources include light guiding panel-equipped light emitting diodes (hereinafter abbreviated as LEDs) and organic light emitting diodes (hereinafter abbreviated as OLEDs) based on the phenomenon of organic electroluminescence (EL).
Light guiding panel-equipped LED light sources have rapidly come into use as general lights and, for example, from around 2008, as backlights for main displays (such as liquid crystal displays) of smart devices (smartphones and tablets), which gain widespread use.
Such LED light sources are used as backlights not only for main displays but also for common function key buttons (what are called software buttons) provided at lower parts of smart devices.
In some cases, for example, such common function key buttons are provided with three marks “home” (indicated by a symbolic mark representing a house), “return” (indicated by an arrow mark or the like), and “menu” (indicated by a three-line mark or the like).
In order to improve visibility, a light guiding panel having a deflection pattern, which is formed in advance depending on the pattern to be displayed, is used for the display on such a common function key button. Light emitted from an LED light source is incident on the end of the light guiding panel, and the incident light is deflected by the deflection pattern to exit in the normal direction of the light guiding panel. In this way, the light is output in a predetermined pattern from the front side of the light guiding panel, so that the emitted light appears in the pattern when the light guiding panel is viewed from the front side (see, for example, Patent Literature 1).
Unfortunately, such a system using a light guiding panel has a problem in that the light incident on the light guiding panel from the LED light source partially leaks from some parts other than the predetermined pattern, so that the efficiency of use of the LED emission is low while power consumption is high.